The present invention relates to a speaker which converts an electrical voice signal to a sound wave. In particular, the present invention relates to a frame for a speaker.
Up to the present time, the material used in the frames of speakers has been metal plate of which thin steel plate, press molded aluminum plate, cast products made from metallic alloys such as zinc or aluminum alloys or products made from injection molding of thermoplastic resins are examples.
For example, FIG. 11 is a cross sectional schematic view of the layout of a speaker unit using metallic plate. FIG. 12 is a front view of an example of a frame used in the speaker in FIG. 11.
In the figures, after a caulking joggle 2a of an upper plate 2 is inserted into a slit 1b formed in the lower end of the frame 1, both components are fixed by a caulking deformation process applied to the top section.
A magnet 4 is sandwiched and fixed between the upper plate 2 and the pole piece 3 by adhesive. It is noted that the magnetic circuit of the speaker is formed by the upper plate 2, the pole piece 3 and the magnet 4.
A gap termed an xe2x80x9cair gapxe2x80x9d 14 is formed between the upper plate 2 and the pole piece 3. A voice coil 5a is disposed in the gap and is wound onto a bobbin 5. The coil 5a generates a sound wave by creating a mechanical displacement due to an input signal and transmits the displacement to a diaphragm 8.
The voice coil 5a wound on the bobbin 5 is supported by a damper 10, an outer section of which is fixed to the frame 1 and by an edge 9, an outer section of which is fixed to the frame 1 in the same way. The center of the coil is arranged so that it moves in the air gap 14 without deviation. The edge 9 is fixed to and integrated with diaphragm 8. A center cap 8a is mounted on the diaphragm 8.
A terminal board 11 mounting terminals 12 is fixed by an eyelet or the like to the other frame 1. Reference numeral 6 denotes a gasket with the functions reinforcing the frame 1 and acting as an interface with the other mounted components.
An input signal from a terminal 12 is supplied to the voice coil 5a through the tinsel cord 13. 1a is a window, 1d in FIG. 12 is a strain absorption hole, 1e is a strain absorption notch.
Generally, metallic plate is widely used in the frames of speakers incorporated in vehicle-mounted music devices or household audio-visual devices due to their excellent qualities and low price. The disadvantage of metallic plate resides in the deterioration of sound quality in the speaker.
The reason for such a deterioration is that self-resonance in the frame is easily induced when the diaphragm of the speaker is oscillated by a sound signal. Furthermore the frequency of such self-resonance is realized in an audible frequency band. Self-resonance is caused by vibration transmitted from the outside to the speaker.
For example, the self-resonance frequency of a speaker with a 13 cm aperture using a 0.7 mm. thickness aluminum frame displays a distribution about 1.5 KHz. Frequencies in the vicinity of 1.5 KHz are faintly audible. That is to say, fidelity is reduced since vibrations of the diaphragm due to the sound signal and the vibration of the frame due to self-resonance become mixed in and are audible.
The problem of self-resonance does not particularly arise in the context of zinc cast products. However casting as a method of fabrication results in cost increases associated with the considerable secondary processing required to achieve a desired shape.
Although resin molded products display superior productivity, generally they have a low mass and share the disadvantage of metallic plate in that self-resonance results from externally applied vibrations.
The simplest method of increasing mass is to increase the thickness of the member. However when this method is applied to the frames of speakers, the outer shape increases together with increases in thickness and thus reduces freedom of disposition of the speaker and poses problems for use m cramped environments such as vehicle compartments.
The relationship of the above materials to environmental protection will be discussed below. When the product life of industrial components expires, it is needless to say that recycling of component materials or disposal with little effect on the environment is desirable. Speakers are no exception to this rule.
Up until the present time, the dismantling and reuse of metallic plate of used speakers has almost never been put into practice. For example, metallic members such as upper plates 2 are fixed strongly by a method such as caulking, adhesion or welding to the frame 1 and thus the subsequent dismantling of these components is physically difficult.
Overall processing costs are created by the processing costs, wage costs and time costs of dismantling the device. Thus even if instituted, such processes showed few economic benefits. Thus used speakers are in actuality usually disposed of in land fills and this as a result represents a waste of resources.
Disposal in land fills is not always an effective method in view of used materials. For example, resin products display extremely low decomposition over time in comparison with metal even when buried in earth or water. Needless to say, this is undesirable from the point of view of environmental protection.
In summary therefore, when molded resin or pressed metal products are used in the frame of speakers, problems with respect to acoustics result even though productivity is excellent. Cast zinc products entail problems with respect to both costs and productivity. Both such products require long periods of time to be decomposed by micro-organisms in the natural world and do not display characteristics oriented to a process of effective recycling or a method of disposal with little effect on the environment.
A known method of manufacturing paper products called fine pulp molding is used in packing containers or packing (i.e. buffer) material as a means of solving the above mentioned problems. Fine pulp molding combines molding and paper manufacturing in a type of manufacturing paper products and is a processing method which creates a three dimensional shape with high levels of accuracy with a pulp material. This method of manufacturing paper products will simply be termed fine pulp molding hereafter.
A characteristic of fine pulp molding is that it is an integrated method of paper manufacturing three dimensional shapes using a combined male-female paper making mold. Another characteristic of the molding is the external beauty of product and it is known for superior characteristics with respect to dimensional accuracy and productivity for paper products having a three dimensional shape.
In addition, the method has the advantage that apart from virgin pulp old paper, disposed paper material such as old paper may be used as material. Thus it is possible to increase the use of old paper which is perceived to create problems of oversupply in the market place and to promote recycling. On the other hand, it is possible to greatly reduce material costs and to reduce manufacturing costs.
An outline of the process of fine pulp molding will be described below. A model of the process is shown in FIG. 13.
Fine pulp molding entails three main sequential steps.
(a) Adhesion step: a male paper manufacturing mold 20 is immersed in a pulp dissolving fluid 23 and pulp is adhered to the male paper manufacturing mold 20 by vacuum suction.
(b) Dehydration/Molding step: a female paper manufacturing mold 21 is pressed onto the pulp which has adhered to the male paper manufacturing mold 20 and dehydration and molding are performed.
(c) Drying step: after pressing and drying with a heated mold onto the pulp which has been shaped by the previous step, the product (pulp mold product 25) is extracted.
Detailed description is outlined below. In FIG. 13, a male paper manufacturing mold 20 is immersed in pulp dissolving fluid 23 filling a pulp vessel 22. The paper manufacturing mold 20 forms an outer shape of the product by the mesh of a fine wire netting or the like. Furthermore the inner section of the male paper manufacturing mold 20 is connected to a vacuum pump 24 through a pipe 26.
(a) In the adhesion step, pulp is adhered to the surface of the mold by suction of air in the inner section of the male paper manufacturing mold 20 having the above shape by using a vacuum pump 24.
(b) In the dehydration and molding step, the male paper manufacturing mold 20 in that state is lifted from the pulp dissolving fluid 23 and the female paper manufacturing mold 21 is compressed. By further suction with the vacuum pump 24, water in the pulp which has adhered during the previous step is removed and the product is shaped.
(c) In the drying step, the mold is maintained in a compressed state and the product is heated and dried by a high temperature heat source such as an electrical drier which is provided in the male-female mold. After completion of the drying process, the mold is opened and the product is removed.
If the manufacture of speaker frames conventionally made from resin molding by injection molding apparatus, or by zinc casting by a casting machine or by metal plate pressing with a metal pressing machine is changed to fine pulp molding, not only are the above advantages obtained, but also advantages with respect to acoustic characteristics and material recycling as outlined below are also obtained.
Generally the self-resonance frequency of paper of equal surface area and equal thickness is known to be lower than the corresponding frequency for metal.
As described above with respect to the prior art, a speaker with an aperture of 13 cm and an aluminum frame of 0.7 cm thickness has a self-resonance frequency in the vicinity of 1.5 KHz. When a paper frame with an equal aperture and a thickness of approximately 2 mm formed by fine pulp molding is used, the self-resonance frequency has been confirmed on the basis of experimental observation to be reduced to the vicinity of 250 Hz.
In this way, since paper reduces the self-resonance point as a result of large internal loss in comparison with metal, it is possible to obtain a speaker with reduced noise on an audible level.
A further advantage is that paper is a non-magnet substance. Steel frames apply a magnetic flux to the frame from the magnetic circuit since the frame is a strongly magnetic body. That is to say, it is not possible to ignore flux leakage which is one reason for reductions in the effectiveness of the device. On the other hand however, a paper frame entails no such considerations.
In comparison to the recycling of a metallic member, speakers using a frame formed by fine pulp molding can be easily separated or dismantled. For example, heating the overall speaker unit to an ignition temperature for paper allows only paper sections to be burnt and metallic members only removed.
Furthermore if the entire speaker is placed in water for a fixed time, the frame will change into a pulp solution. In this way, easy of disassembling or dismantling allows costs for the recycling of paper frames to be held to low levels.
Disposal by way of burying, for example in simple land fills, can be advantageously used for paper frames in comparison with other materials. The decomposition of paper in earth is completed in a short period of time by bacteria as is the case with timber. This equals a low effect on the environment. On the other hand, steel frames take a long time in comparison with paper frames and resin frames are almost impervious to decomposition even after the passage of extremely long periods of time.
The present invention relates to fine pulp molding which is an excellent processing method and material for the frames of speakers as discussed above. However for the reason detailed below, such processing has not been carried out.
Fine pulp molding entails the compressing and heating of plant fiber which is dissolved in an aqueous solution and flows onto a mold. Thus problems with respect to the dimensional accuracy of the product which are typically associated with metal pressing or resin molding are avoided.
A speaker requires metallic members comprising a magnetic circuit such as an upper plate and a bottom plate apart from the frame. These are secured and maintained at a fixed accuracy to a fixed position on the frame. For example, a plurality of slits 1b of a required accuracy must be provided on an upper face of the frame.
Since fine pulp molding of itself does not obtain an accurate outer shape or a required accuracy for the interval between mutual holes or the hole radius, secondary processing has been used in conjunction with fine pulp molding as an auxiliary means.
Shear processing by pressing becomes increasingly difficult with increases in the cross sectional thickness of paper material. Many pulp fibers which are mutually matted in shear surface cross section are not easily ruptured and as a result, a clear cut cross section is not obtained Thus when shear processing is conducted on a mass production basis, wear on apparatus such as cutting dies is increased and the cut face becomes increasingly coarse.
In consequence, the time required for maintenance and preparation of apparatus increases which at the same time reduces productivity. When pulp consisting of long length fibers is used, the above tendency is particularly pronounced. The most conspicuous difference between press shear processing of paper and shear processing of metal plate resides in this point. It is necessary to address this poor processing efficiency in order to produce speaker frames with fine pulp molding.
The problem of frame strength has also arisen with respect to extreme environments. Speakers for use in general household audio-visual appliances are sufficiently strong, however it is believed that frame strength is deficient in environments with high temperature and humidity or high levels of vibration such as vehicle mounted audio products for example.
As discussed above, specific advantages and disadvantages exist for the quality of frames for use in speakers and many problems remain to be solved with respect to sound quality, cost, reliability, recycling of materials and disposal processing.
The present invention is proposed to solve the above problems and has the object of providing a frame for use in speakers which, as a result of improvements to the fine pulp molding manufacturing process, realizes excellent sound quality at a low cost, which allows recycling of materials and which reduces effects on the environment due to facilitating disposal.
(1) The speaker device of the present invention proposes a speaker which forms a frame from pulp by a paper manufacturing process. A peripheral section of the shear processed section of the frame is carbonized and shear processing is then applied to the carbonized section.
(2) The speaker which forms a frame from pulp by a paper manufacturing process provides sections which are selectively heat pressed and sections which are selectively not heat pressed in the frame. At least a peripheral section to a mounting hole provided in the frame is designated as a section which is not heat pressed.
(3) A speaker which forms a frame from pulp by a paper manufacturing process embeds at least one section of an auxiliary strengthening member in a peripheral section of a mounting hole on the frame and mounts the auxiliary strengthening member on a peripheral section of a mounting hole.
(4) The speaker which forms a frame from pulp by a paper manufacturing process embeds at least one section of the upper plate in the frame and mounts the upper plate on the frame.
(5) The speaker which forms a frame from pulp by a paper manufacturing process forms an electrically insulated section by impregnating an insulating medium such as an insulating oil at least into the terminal mounting section of the frame and mounts the terminal.
(6) The speaker which forms a frame from pulp by a paper manufacturing process is composed of pulp and a material which comprises biodegradable fiber having a relative density near that of pulp.